It might be too late to implement anything new, but still I'd like to suggest something concerning the slot shortage:

What about stacks for slots in the hotbar?

By that I mean something like right clicking over any slot to display above it a list of skills of the same type as the one currently equipped. For example, with Flare equipped in slot 1 a right click over it would display a stack of all my learnt fire elemental skills. Then I could choose any of them to replace it with a single click. The same would happen for skills from other schools of magic and could even work for scrolls, potions, consumables... Each item type appearing as stacks in a manner not so different from the interface of DD.

That way a wizard could have his/her hotbar equipped with all four elementals in slots 1-2-3-4, witchcraft in the fifth, have one slot for potions, one for scrolls, one for consumables and still have two free slots left for any personal preferences or even warrior/ranger skills.

Simple and easy as that! No dragging, no hotbar cycling or the like.
And of course it would be possible to do the same in the second and third bars for even more flexibility.

What do you guys think?